The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one disk (such as a magnetic disk, magneto-optical disk, or optical disk), a spindle motor for rotating the disk, and a head stack assembly (HSA). The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly includes at least one head, typically several, for reading and writing data from and to the disk. In an optical disk drive, the head will typically include a mirror and objective lens for reflecting and focusing a laser beam on to a surface of the disk. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The spindle motor typically includes a rotatable spindle motor hub, a magnet attached to the spindle motor hub, and a stator. Various coils of the stator are selectively energized to form an electromagnetic field that pulls/pushes on the magnet, thereby imparting a rotational motion onto the spindle motor hub. Rotation of the spindle motor hub results in rotation of the attached disks.
The head stack assembly includes an actuator assembly, at least one head gimbal assembly, and a flex circuit assembly. A conventional “rotary” or “swing-type” actuator assembly typically includes an actuator having an actuator body. The actuator body has a pivot bearing cartridge to facilitate rotational movement of the actuator assembly. One or more actuator arms extend from the actuator body. The configuration of an actuator body and actuator arms is sometimes referred to as an “E-block.” Each actuator arm supports at least one head gimbal assembly that includes a head. An actuator coil is supported by the actuator body opposite the actuator arms. The actuator coil is configured to interact with one or more magnets, typically a pair, to form a voice coil motor. The printed circuit board assembly selectively controls current passing through the actuator coil that results in a torque being applied to the actuator.
A latching mechanism is provided to facilitate latching of the actuator in a parked position when the heads are not being used to interact with the tracks on the disk. In the parked position, the actuator is positioned with the heads either at an outer diameter (OD) or inner diameter (ID) of the disk. A crash stop coupled to the disk drive base is provided to limit rotation of the actuator in a given direction. The crash stop is configured to contact a portion of the actuator when the actuator is rotated in a given rotational direction. Another crash stop may be provided to limit actuator rotation in an opposite rotational direction. The latching mechanism may additionally function as one of the crash stops.
Some contemporary actuators use a coil that is coupled to an actuator body through the use of a plastic overmold. For example, a machined metal E-block and an actuator coil may be overmolded with plastic that encircles a coil. Such a design is subject to thermal dissipation problems at the coil and the surrounding overmold plastic. Since the coil and overmold materials typically have grossly dissimilar coefficients of thermal expansion, the temperature swings exacerbated by thermal dissipation problems can cause higher stresses which, in turn, may lead to thermally induced mechanical instability. For example, such thermally induced mechanical instability may include an undesirable stick-slip phenomenon known as “coil popping.” In contrast, so-called “bonded coil” designs do not use a plastic overmold and therefore are not subject to the same degree of thermal gradient. However, traditional bonded coil designs may have other disadvantages in certain applications, such as manufacturability, bond strength, and cost.
Accordingly, it is contemplated that there is need in the art for an improved bonded coil actuator configuration.